Circuit breakers are one of a variety of overcurrent protection devices used for circuit protection and isolation. The circuit breaker provides electrical protection whenever an electric abnormality occurs. In a circuit breaker, current enters the system from a power line and passes through a line conductor to a stationary contact fixed on the line conductor, then to a movable contact. The movable contact can be fixedly attached to a pivoting arm. As long as the stationary and movable contacts are in physical contact, current passes from the stationary contact to the movable contact and out of the circuit breaker to down line electrical devices.
In the event of an overcurrent condition (e.g., a short circuit), extremely high electromagnetic forces can be generated. The electromagnetic forces repel the movable contact away from the stationary contact. As shown by an example of a prior art circuit breaker in FIGS. 1A and 1B, the circuit breaker 10 includes a stationary contact 30, a moveable arm 35, a cam follower 50, a crossbar 60 and a shunt 40. Because the movable contact 35c is fixedly attached to the rotating arm 35, the arm 35 pivots and physically separates the stationary 30 and movable contacts 35c, and the current is stopped as the breaker mechanism moves to the tripped position.
Upon separation of the contacts and blowing open the circuit, an arcing condition occurs. The breaker's trip unit will trip the breaker which will cause the contacts to separate. Also, arcing can occur during normal “ON/OFF” operations on the breaker.
During a high interruption shot on the breaker (e.g., an EG breaker, where “E” reflects breaker size, and “G” represents the breaker is part of the “G” or global series), the shunts are pulled together by the electrically generated magnetic fields. The contact arm also rotates during the high interruption shot. As shown by the desired normal off configuration of the crossbar 60 and arm 35 in FIG. 1A compared to the configuration in FIG. 1B, sometimes the shunt 40 undesirably travels to a position on top of the contact arm 35 which prevents the arm from fully resetting after the interruption terminates and the mechanism rotates the crossbar 60 to the tripped position. This then prevents the breaker from making contact when the breaker is closed.